The present invention relates to display devices and system. More particularly, the present invention provides all-metal electronics for such devices and systems. Still more particularly, embodiments of the present invention provide all-metal electronics which may be formed directly on the surface of a display panel.
There is growing awareness of the need for increased functionality of device/circuit technology based not on the decrease of minimum feature size, with its attendant increase of infrastructure costs (roughly doubling at every other technology node), but rather on constraints arising from needs requiring larger areas (macroelectronics). A typical example is a liquid crystal display (LCD) where system size is dictated by the scale of the image accessible to human vision. In view of the utility of the LCD as an exemplary display type, much of the following discussion will be framed with reference to LCDs. However, it will be understood that macroelectronics encompasses a significantly wider set of applications.
The challenge facing current macroelectronics technology is that many applications call for deposition on surfaces other than crystalline silicon. However, state-of-the-art transistors cannot be built on anything other than a crystalline silicon substrate. Two different approaches are presently being taken by the industry to address this problem. Both use silicon variants for the circuitry.
With reference to the display industry, an LCD that can actively control each subpixel (and therefore each pixel) separately is called an active matrix liquid crystal display (AMLCD). Building silicon-based electronic circuits on the glass panel of an LCD presents difficulties in that crystalline silicon cannot be grown on glass.
One approach to fabricating AMLCDs uses polysilicon technology to build thin-film transistors (TFTs). The problem with this approach is that TFT performance is severely degraded compared to that of crystalline transistors. This is mainly due to the very low mobility of electric charges in polysilicon material and the wide dispersion of functional parameters. As a result, the quality of polysilicon transistors is not high enough to build ancillary electronics directly on glass.
A more promising technology currently being developed is to use a polysilicon variant called continuous-grain silicon (CGS) to build the driver transistors directly on glass. The developers expect that this technology will allow building memory cells and ancillary electronics on glass as well. CGS transistors offer a higher level of quality than polysilicon transistors, but are still significantly inferior to the crystalline silicon transistor. As a result, current AMLCD solutions typically implement selection and driver electronics, as well as the frame memory blocks, in separately manufactured silicon ICs which are then attached to the glass panel by using chip-on-glass technology. Thus, only the pixel-controlling transistors are built directly on glass.
The necessity for using chip-on-glass techniques increases manufacturing costs and requires wiring to connect these electronic components to the pixel-controlling transistors. This degrades the analog signals as they must travel at least half the distance of the display dimension. Several companies have now been working on this technology for more than a decade.
The performance and potential of both polysilicon and continuous grain silicon are thus seriously limited. Therefore, there is a need is for display technologies which overcome these limitations.